1. Field of Invention
This invention relates to an energy management and other automatic control systems employed in a deionizer system that can remove charged species from liquids automatically and continuously with recovery of the process energy. More specifically, this invention relates to ion removal systems using capacitive deionization (CDI) on a number of flow-through capacitors (FTCs) in conjunction with supercapacitors, ultracapacitors, or electric double layer capacitors as the energy-storage device for storing the electrical energy that is reclaimed during the regeneration of FTCs.
2. Description of Related Art
There are numerous pollutants of inorganic, organic, or biological nature in the contaminated liquids and waters. Many methodologies and techniques can be used to decontaminate the impure fluids, nevertheless, none of the methods is universal. Among the pollutants, charged species or ions are probably the most frequently occurring source of contamination. This is due to that the contaminants often dissolve as ions, or they are dissociated or hydrolyzed into ions in the liquids. In either case, the contaminants are described as total dissolved solids (TDS) measured in ppm (parts per million). It requires a special treatment other than a simple filtration to reduce the TDS to acceptable levels for use or discharge. No matter what method is adopted, it should fulfill the following requirements: 1) low cost, 2) high efficiency, 3) no secondary pollution, 4) robust, and 5) energy efficient, for a method to become a cutting-edge technique on purifying liquids.
Ion-exchange and reverse osmosis (RO) are presently two popular techniques utilized for the reduction of TDS. Before applications, ion-exchange resins must be pre-conditioned in chemicals such as strong acids or bases followed by rinsing with copious de-ionized water. Strong chemicals and high-quality water are also used to regenerate the resins. Regeneration of ion-exchange resins can only be repeated in a limited number of cycles as the resins are vulnerable to degradations. Therefore, ion-exchange method is wasteful in terms of consuming chemicals and water, and the process generates secondary pollutions during precondition and regeneration of the resins. Opposite to the natural migration of solvent in osmosis, pure solvent is transferred from the high concentration side to the dilute side through fine pores of RO membranes in RO operation. To counteract the osmotic pressure, which is existent in all solutions and increases with the concentration of solutions, RO requires the application of pressures on the RO membranes for extracting the pure solvent from solutions. Therefore, the process energy of RO is high, which is also aggravated by most liquid is not recovered, and pollutants are left behind making the original liquids more polluted. As the pores of RO membranes are so fine, for example, 0.5 xcexcm, that they are prone to fouling, as a consequence, they rely on costly pre-treating setups for protection. Regeneration of the RO membranes is also wasteful by consuming chemicals and pure solvents without mentioning the generation of secondary pollution.
Since TDS is associated with charged species, electro-technology, especially capacitive deionization (CDI) is a more sensible method than ion exchange and RO on reducing the ionic wastes. CDI utilizes the configuration of capacitor, or a flow-through capacitor (FTC) to be specific, wherein an electrostatic field is built with the application of low DC voltages to the electrodes for adsorbing ions as the ion-containing liquids flow through the electric field. Electricity is used to modulate the removal of ions, or purification of liquids, containing many adjustable parameters that impart CDI considerable maneuver-abilities.
There are many CDI and FTC works granted in the US patent publications, some typical examples can be found in U.S. Pat. Nos. 3,515,664, 3,658,674, 5,425,858, 5,514,269, 5,766,442, 6,022,436, 6,325,907, 6,346,187, 6,410,428, and 6,413,409. They are all incorporated herein by reference. Though various fabrication methods of electrodes and electrode modules, as well as miscellaneous patterns of liquid-flow, are disclosed in the prior art, they are generally lack of an implementing methodology to become commercially viable on treating massive liquids. One of the miscomprehended arrangements of conducting CDI in the prior art is that the fundamental properties of capacitors, for example, fast charging and fast discharging, are overlooked. In essence, the adsorption of ions on the electrodes of CDI module is the same process as the charging of capacitors, while desorption of ions from the CDI electrodes is equivalent to the discharging of capacitors. As the charging and discharging of capacitor normally take place in a matter of seconds, as well as repeat in numerous cycles, the ion-adsorption and ion-desorption of CDI technique should be conducted swiftly without unduly delay. Furthermore, energy is harvested at capacitor discharging because that is the reason that energy is invested at charging. Thence, energy can be reclaimed as a by-product at the regeneration of the CDI electrodes. Unlike ion-exchange and RO, no chemicals and pure solvents are consumed, nor secondary pollution is generated during the regeneration of CDI electrodes. It is due to that low process energy is used for deionization, energy is recovered at regeneration, and the foregoing processes are rapidly completed that transforms the CDI technique into a method of low cost and high productivity for environmental applications.
The present invention provides an implementing method of automatic CDI for commercially producing fresh water via desalination or recycling waste waters, for liquid waste reduction, and for other high value-added applications.
Both ion adsorption on the electrodes of CDI modules and regeneration of the CDI electrodes are fundamental physical processes in the nature. While the surface adsorption is due to electrostatic attraction, the electrode regeneration occurs by means of static-charge dissipation, just like the charging and discharging of capacitors, the two processes of CDI will respond promptly and reversibly to the external actuations. It is the intent of the present invention to devise a fully automatic system utilizing the foregoing physical processes for producing fresh water, pure solvents, and useful resources with a high energy-efficiency. In accordance with the present invention, one object is to use an economical material as the active adsorbent of ions. First of all, the material should be adsorptive, conductive and inert in adverse conditions such as strong acids, strong bases, strong oxidants, and organic solvents. Among many choices, activated carbons (ACs) are one ideal group for CDI applications. Unless added benefits to justify the extra efforts put on preparing extraordinary carbonaceous materials, otherwise, an inexpensive and commercially available AC is good enough for some CDI applications. Using conventional means, for example, roller coating, and with the assistance of a binder, powder of an ordinary activated carbon can be attached to a metallic support forming the electrodes of CDI.
Another object of the invention is to construct the electrode modules of CDI in a simple and effective assembly. All modules should allow free path to liquids as in regular FTCs. In order to attain high adsorption efficiency, all of the impure liquid must be subjected to the static electric field built within the electrode modules. This means that the fluid must pass between the charged electrodes and there is no bypath for the un-treated liquid to escape, as well as no concealment in the container of FTC for the liquid to remain un-treated. Thus, simple assemblies as normally used for capacitors, for example, spiral winding and parallel stacking, are adopted to make FTCs to fit into the housings of desirable shapes and dimensions in a liquid-treating system. To fit the shapes of various housings, the electrode module can be in the form of cylinder, cube, or rectangle. Hermetic sealing and flow guides are provided in the treating units comprised of FTCs and housings to ensure the requisite pattern of liquid flow.
Following the completion of CDI treating units, there should have an energy manager to govern the reciprocating deionization and regeneration, or charging and discharging, of the electrode modules for purifying liquids. It is yet another object of the invention to devise an energy management sub-system comprising of a DC power source, an energy-storage device, and a micro-controller that allows the settings of various durations for conducting either deionization or regeneration as desired. Electricity is supplied to the electrodes from the power source for deionization, whereas the residual energy of the electrodes is released to the storage device during regeneration. Both processes should be modulated to continue for appropriate durations without unduly delay. Also, the DC voltage is controlled at a level only to sustain an electric field for electrostatic attraction of ions, rather than causing electrochemical reactions.
Yet another object of the invention is to devise an automation sub-system comprising of a micro-controller, on-line sensors and electromagnetic fluid values. As the sensors detect the purity of effluent of a particular CDI treating unit below a predetermined level indicating the requirement of regeneration, upon a signal from the sensors, the controller will divert the flow-direction of electromagnetic valves so that the influent can be changed from liquid to be treated to the regeneration liquid. At the meantime, the electrode module will automatically be converted from deionization to regeneration, or from charging to discharging. All of the on-line monitoring, liquid-flow diversion, and energy transfer can be programmed to set up a desirable sequence of events, and as many cycling times of treatments as necessary without human attention.
Still another object of the invention is to devise a fully automatic CDI setup as a pre-treatment for the more expensive and fragile liquid-treating equipment such as ion-exchange and RO. CDI is capable of directly purifying high-concentration liquids such as seawater, so the TDS of liquids can be reduced to the suitable levels for ion exchange and RO that the service life of the latter can be prolonged. Because of the low cost of materials used, energy-efficiency of operation and pollution-free characteristics, the fully automatic CDI system of the invention can offer cross cutting benefits to the waste reduction of various liquids.
A further object of the invention is to devise a fully automatic CDI setup to recycle useful resources for reuse. During the regeneration of CDI electrode modules, a rinsing liquid is employed to transfer the desorbed ions, the ionic contaminants that are removed from the liquids at deionization, to a designated reservoir wherein useful resources can be concentrated and recovered. Not only the sludge from the purification treatment is easy for disposal, the present invention also provides values added to the reduction of liquid wastes by recycling useful resources for reuse in an economical fashion.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.